燃气一蒸汽联合循环热力性能良好,但其能源利用率远未达到最大值,仍具有 提高潜力。天然气燃烧产生的烟气中水蒸汽容积分数较大且基本不含so2,所以降 低循环放热温度,回收烟气潜热,是提高能源利用率的有效途径之一。本文针对燃 气一蒸汽联合循环潜热回收问题,从理论上进行可行性研究。 首先,以河北某燃气一蒸汽联合循环电站为研究对象,分析燃烧后产生的烟气, 比较可以回收的烟气显热和潜热的数量关系,分析其在不同排烟温度下的变化趋势, 并分析烟气在热力平衡条件下的凝结特性。 其次,考察了含有少量水蒸汽的混合气体对流冷凝换热的机理,重点讨论水蒸 汽容积分数在6%?15%范围的换热情况。利用膜模型分析相界面附近扩散膜内的质 量、热量和动量传递特点,利用热量与质量传递的类比关系,同时考虑质量传递引 起的附加速度的影响下,提出含湿烟气对流显热换热与凝结潜热换热模型,导出描 述现象的微分方程,并求解获得气膜内速度、浓度和温度分布及液膜内的速度分布。 对对流传热传质过程进行无量纲分析,得到无量纲数一冷凝因子的传热准则关联式, 利用关联式求凝结传热膜系数。 根据余热锅炉给水吸热的平衡关系,使用锅炉给水作为低温介质不能将排烟温 度降至露点温度以下,导致冷凝式换热器中水蒸汽冷凝比例非常小,烟气余热回收 量非常有限;针对此问题,提出了烟气潜热回收的新思路,将冷凝式换热器与蒸汽 型双效溴化锂吸收式热泵相结合,将吸收式热菜低温热源循环水(回水25°C)作为 冷凝式换热器的低温介质,设计出利用烟气余热加热热网水的热电联供系统。并分 析了该系统的节能效益与环保效益,结果表明该热电联供系统可有效回收烟气潜热, 与改进前机组额定供热工况相比,汽轮机抽汽量减少30%,汽轮机发电功率提高 11.32%,供热能力提高53.66%,天然气利用率显著提高。针对系统存在问题,探讨 了不同凝结换热强化手段的可行性及强化效果。 关键词:湿烟气,潜热回收,凝结换热,热电联产 I 华北电力大学硕士学位报告 Abstract The performance thermal of Gas - steam combined cycle is good,but the energy efficiency is far from the maximum, and it's still has the potential to increase. The flue gas due to combustion of natural has large proportion of water vapor and substantially free SO2, so reducing the temperature of cycle heat and recycling the latent heat of flue gas can effectively improve energy efficiency. Aiming gas - steam combined cycle latent heat recovery problem theoretically conducted systematic research. First, according to Hebei fueled with natural gas components, we can conduct combustion calculations, and then analysis the flue gas produced by combustion. Through comparing the recycled flue gas sensible heat and latent heat relationship we can analyze the trends in different exhaust gas temperature and analysis the condensation characteristic of flue gas under equilibrium conditions. Second, investigating the condensation heat transfer mechanism of mixed convection gas in which containing a small amount of water vapor, which focusing on the volume fraction of water vapor in the range of 6% to 15% of the heat transfer case. Analyzing transfer characteristics of mass, heat and momentum inside diffusion film near the Phase boundary by using film model. If using the analogy relations about heat and mass transfer and taking into account the impact of additional speed caused by the mass transfer, then we can propose convective sensible heat exchanger of flue gas which contents moisture and latent heat of condensation heat transfer model. Export describing the phenomenon of differential equations and solve to get gas film speed,concentration and temperature distribution and velocity distribution within the fiim. Of the convective heat and mass transfer process dimensionless analysis, the dimensionless number - condensing heat factor associated guidelines, the use of relational seeking condensation heat transfer film coefficient. According to the Endothermic balance of the heat recovery boiler feed water, exhaust temperature cannot reduce to a temperature below the dew point by using boiler feed water as cryogenic medium, which resulting in water vapor condensation takes very small proportion in heat exchanger and the quantity of flue gas heat recovering is very limited. For this problem, put forward a new idea of recovering flue gas latent heat. It is 华北电力大学硕士学位报告 said that combining the condensing heat exchanger and double-effect absorption heat pump to use the low-temperature circulating water (backwater 25 °C) of heat absorption heat pump as cryogenic medium of condensing heat exchanger to design a heating hot water cogeneration system which utilizing the waste heat to heat network water . Analysis the economic and environmental benefits of the new system, the results show that the new system can effectively recycle flue gas latent heat. The new system can reduce by 30% the amount of extraction steam turbine, the steam turbine power generation improved 11.32% in rated extraction conditions, heating capacity increased by 53.66%, which shows that the utilization of natural gas significantly improved. For system problems, exploring feasibility and strengthening effect of different means of condensation heat transfer enhancement. Key words: wet flue gas, latent heat recovery, condensation heat transfer, cogeneration. Ill 华北电力大学硕士学位报告 目录 m w I Abstract II 第1章绪论 1 l.i研宄背景及意义 1 l.i.i我国能源利用现状及环境问题 1 1. 1.2研究意义 2 1.2国内外研宄现状 4 1.2.1国内外燃气蒸汽联合循环技术发展现状 4 1.2. 2烟气潜热利用研宄现状 5 1.2.3混合气体的凝结理论研宄现状 6 1. 3本文主要工作 8 第2章联合循环烟气分析及余热潜力计算 9 2.1联合循环烟气计算 9 2.1.1燃料成分及热物性 9 2.1.2燃烧计算 11 2. 2烟气的热力平衡冷凝特性 13 2.2.1热力学冷凝曲线 13 ‘2.2.2烟气中水蒸汽的理论冷凝率 14 2. 3烟气余热潜力计算 15 2. 3.1烟气显热损失 15 2. 3.2烟气潜热损失 18 2. 4本章小结 19 第3章烟气管外对流冷凝换热分析 20 3.1烟气对流冷凝换热传热传质的类比 20 3. 2模型控制微分方程 22 3. 2.1质量传递 23 3. 2. 2热量传递 25 III 华北电力大学硕土学位报告 3.2.3液膜内温度分布、速度分布 25 3. 3理论计算 27 3. 4无量纲关联式 27 3. 5本章小结 28 第4章烟气潜热回收热电联产系统 29 4.1烟气潜热回收热电联产系统 29 4. 2冷凝式换热器设计 31 4. 3冷凝式换热器效益分析 32 4. 3.1节能效益 32 4. 3. 2环保效益 33 4. 4增压冷凝过程 34 4.4.1气体状态改变 34 4. 4. 2增压效果 35 4. 5凝结换热强化 37 4. 5. 1粗糖表面法 37 4. 5. 2扩展表面法 38 4. 6本章小结 38 第5章结论与展望 40 5.1主要结论 40 5. 2工作展望 40 職 42